Technical Abstract:
Moderately low temperatures (12-15 deg C) that often prevail in short-season temperate climates during the early crop growing season can greatly restrict vegetative growth of maize (Zea mays L.), hence reducing grain yield potential. Cold-induced growth inhibition is often associated with reduced photosynthetic capacity, but variation of this response exists among maize genotypes. Theoretically, reduced growth under low temperatures could cause sugar accumulation in source leaves triggering feedback inhibition of photosynthesis. Two maize genotypes differing in their growth sensitivity to low temperatures were field-sown in early and late spring in west central Minnesota, USA. When sown early, leaf photosynthesis, Rubisco and PEPcarboxylase activities were greater in the cold tolerant genotype, and were similar to those of plants developed from the later sowing. Both genotypes sown in early spring showed a similar diurnal trend in soluble sugar flux in mature leaves at the V2 stage. However, the cold tolerant genotype partitioned 71% more nonstructural carbohydrates to roots than the cold sensitive cultivar. Results indicate that differences in photosynthetic capacity between the two maize genotypes to growth under low temperatures was not related to leaf soluble sugar content, but rather to sink strength and capacity, particularly in roots.